I've never heard of anyone vomiting N but I'm no expert
I saw a post, possibly a while back, that someone did vomit or possibly spew while drinking N because of the ethanol taste - I saw that post while doing some search about N. They said they made two mistakes and I took notes somewhere. I think they reattempted and ctb the following day.
https://sanctioned-suicide.net/threads/goodbye-with-n.91109/post-1614323
Risperdead said they "couldn't chug it down, vomited". No antiemetics. One of the users I was thinking of, possibly not the same as the other one who mentioned two mistakes and ethanol taste.
I think if you don't want to risk ringing alarm bells, as long as you have enough N you might not need anti-emetics. I had similar thoughts, I thought about getting some of the required drugs separately instead of all at once.